We like to think obsessive food cravings that hijack our brains till we can’t focus on anything else are our bodies’ clever way of letting us know we’re low on key nutrients (chocolate does contain magnesium) and need to refuel. In some cases that may be true. Hard-core athletes may crave protein or salt because they need to rebuild muscle and replenish electrolytes after an intense workout. Pregnancy (rare after 50, but becoming more of an option with infertility treatment advances), with its changing hormones and increased nutrition needs to support the baby’s development, brings all sorts of strange desires for certain foods.

The same goes for any kind of extreme dieting that puts the body in starvation mode. If you’re severely iron-deficient (also rare as you age, but possible), you may get bizarre urges to devour ice, laundry starch, chalk, paper, even rubber bands, dirt or clay — a throwback, perhaps to the iron sources our caveman ancestors had available.

“Start with the presumption that the true, original `value’ in cravings relates to survival,” explains Dr. David Katz, director of Yale University’s Prevention Research Center in New Haven, Conn. “Iron is a soil nutrient, so chewing on clay or gritty material may mimic the original source of iron for our ancestors. The craving may persist because those who had it benefited from it. This is conjecture, but it makes sense.”

In situations like these — extreme physical exertion or deficiency — cravings are signals of true nutritional need. “You’re tapping into a Stone Age conversation with your body,” Katz says. “Most cravings that persisted and were passed along are those that increased survival because they were about genuine need, in general or for specific nutrients, and the cravings drove our ancestors to satisfy that need. Those who did were more likely to survive and pass their genes on than those who didn’t get the craving and ignored the cause.”

Want vs. Need

That Stone Age conversation might have made sense millions of years ago. But for the most part it is not meaningful in our contemporary culture, with readily available sources of fast, cheap, tasty calories. So while nutritional “need” might sound like a good excuse for cravings and overindulgence, most cravings aren’t driven by need. They’re driven by want.

“The cravings most people get now cannot be trusted because the modern food environment has co-opted the Stone Age programming,” Katz says. Take the craving for sweets, for example. To some extent, “we are hard-wired to crave sweets because there were few sources of concentrated sugar in the Stone Age,” he says. “At birth, there was breast milk, and after that there was honey and fruit, which are excellent sources for quick, readily metabolized energy. But there was no way to overeat them. In the modern world, we get too much sugar. That leads to tolerance, and cravings become exaggerated.

“The same is true of sodium. The more you salt your food, the saltier you want your food to be and the more likely you are to crave salty foods. With cravings, the more you get, the more you want. But that’s not physiologic need.”

This isn’t surprising since addiction research suggests that the foods we crave most — processed foods, high in sugar, fat, salt and calories — hit the brain’s reward centers just like cocaine, alcohol and cigarettes do. They trigger the release of dopamine, which can make us crave those foods even more — especially if cravings strike when our mood is low or stress is high.

Martina Cartwright, adjunct professor of nutrition sciences at the University of Arizona, explains how it works: Under stress, our bodies pump out large amounts of cortisol, a stress hormone that not only makes us hungry; it makes us hungry for fatty, sugary foods in particular. Eating those foods under stress releases dopamine, which makes us feel better. Our brains remember that association, and the next time we feel frazzled, we reach for the food that eased the stress or improved our moods before. As that becomes our pattern, the reward we get from the dopamine release in itself triggers cravings, closing the loop on a cycle that ultimately leads to overeating: The more stress we’re under, the more we crave the foods that make us feel better, and the more dopamine is released when we eat those foods, the more we crave the foods that we know release dopamine.

Likewise, people who have always consoled themselves with a specific food will crave that food when sad or blue. “You want a certain thing because you want to feel a certain way and there’s a certain thing you’ve eaten before that made you feel that way, therefore you want that thing,” Katz says. This also explains why people crave such a variety of foods. “For one of my clients, it was banana bread,” Cartwright says. “Nothing else satisfied her emotionally, because as a child, she was always given banana bread when she was unhappy.”

The Role of Memories and Habits

Why does one person crave chocolate or ice cream while another craves fries or chips? Researchers believe the differences are related to several factors: cultural background (chocolate and pizza top the list of most-craved foods in the United States while Egyptians tend to crave savory fare like eggplant stuffed with meat); gender (women reach for sweets, while men crave salty snacks); and eating habits picked up in childhood and reinforced over a lifetime. Guys in particular, says Cartwright, tend to crave the comfort foods — macaroni and cheese, mashed potatoes and meatloaf — that their moms used to make.

“Sensory memories and habits play a big role in cravings,” explains Marcia Pelchat, a food psychologist and researcher at Monell Chemical Senses Center in Philadelphia. Brain scan studies show that brain regions associated with emotion, habit and memory of how an activity feels light up when people experience cravings. “People crave foods they’ve actually had, and they have a sensory template for what they need to experience for the craving to be satisfied.”

Eating popcorn at the movies is the classic example, she says. If you’ve always eaten a tub of popcorn at the multiplex, simply going to the multiplex will trigger a desire for popcorn. “Popcorn is particularly potent” because you see it and you also smell it,” Pelchat says. “Aroma is arguably more influential because it’s harder to escape. You continue to experience the aroma even in the dark theater.”

Curbing Cravings

These five steps can help conquer your cravings.

Blog about it or write in a journal. Writing about what you’re feeling when your cravings hit may offer clues to any patterns between your emotions and certain foods.

Wait it out. Take a walk, update Facebook, phone a friend, fold some laundry. Distracting yourself buys time for the craving to pass. “Finding something else to do may make you feel better or forget your craving temporarily, but most importantly, it weakens that automatic link between thinking of food and eating it,” Pelchat says.

Make it hard to get. Studies done at Cornell University’s Food and Brand Lab show that the more inconvenient it is to get a food, the less of it you’ll eat. So don’t keep trigger foods in the house. Move the candy dish off your desk. Wrap brownies in foil, then bury them in the back of the pantry.

Get a kid-sized portion. Some people need to go cold turkey, but for others, complete denial just makes cravings stronger. In that case, allowing yourself small portions, even daily, of your food of choice may curb the craving.

Eat with your non-dominant hand. In University of Southern California studies, popcorn eaters at the movies who ate with their opposite hands, consumed about 13 percent less — and eating less reduces the craving.